Which one of the following is not used as raw material in the manufacture of glass ?
- A.Soda
- B.Alumina
- C.Borax
- D.Gypsum
Correct answer
Explanation
The correct answer is D, Gypsum. Gypsum (calcium sulphate dihydrate) is not a raw material for glass; it is added to cement to slow down its setting.
Glass is made by melting silica (sand) with soda (sodium carbonate) and limestone, and other substances are added for special kinds of glass. Borax supplies the boron oxide of heat-resistant borosilicate glass, and alumina makes glass tougher and more durable. Colours come from metal oxides, such as cobalt oxide for blue and chromium oxide for green. Gypsum, when heated, gives plaster of Paris.
A is not the answer: soda (sodium carbonate) is one of the three main raw materials of ordinary glass.
B is not the answer: alumina is added to many glasses, such as glass fibre, to improve strength and resistance to chemicals.
C is not the answer: borax is the source of boron in borosilicate (pyrex) glass.
Exam tip: glass = sand + soda + limestone; gypsum goes into cement and plaster of Paris.
Practice Questions
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Show answer
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